The human skeleton is made up of 206 bones. The bones, also called osseous tissue, are a type of hard endoskeletal connective tissue that supports body structures, protects internal organs, and (in conjunction with muscles) facilitates movement. Unfortunately, bones are subject to fracturing as a result of physical trauma or certain medical conditions that weaken the bones, such as osteoporosis or certain types of cancer. Although fractured bones can heal by natural processes, it may sometimes be necessary to reinforce or stabilize the bones with metal implants during the healing process.
More importantly, replacing a joint affected by osteoarthritis (“OA”) with a prosthetic device is a common procedure. OA is a degenerative joint disease characterized by progressive break down of the cartilage matrix. Cartilage is the part of the joint that cushions the ends of the bones and allows easy movement of joints. It also absorbs energy from the shock of physical movement. The breakdown of cartilage causes the bones to rub against each other, causing stiffness, pain and loss of movement in the joint. OA affects approximately 21 million Americans a year, accounting for 25% of visits to primary care physicians. It is estimated that 80% of the population will have radiographic evidence of OA by age 65 with more than 60% of those exhibiting symptoms.
If the joint does not respond to conservative treatment such as medication, weight loss, activity restriction, and use of walking aids such as a cane, joint replacement with a prosthetic device is considered appropriate. The most common joints to be replaced are knees and hips. About 435,000 Americans have a hip or knee replaced each year. Research has shown that joint replacement can help even older patients to move around and feel better. For a joint replacement to succeed, the prosthetic replacements require rapid bone ingrowth in them to stabilize the implant and allow the patient to resume the normal activities of daily living.
The mechanical disturbance of the bone after fracture or during surgery may, however, delay its repair and regeneration resulting in transient instability of the implant. In addition, it may lead to a fibrous tissue interposition between the bone and the implant which may lead to loosening of the implant. Loosening of the joint is the most common cause of failure in hip joints that are not infected. This may require another joint replacement surgery in about 12% of patients within a 15-year period following the first procedure. Thus, younger patients may need to have the same damaged joint replaced more than once.
Prior attempts have been made to modify the surface of orthopedic implants with biological substances to promote faster bone repair and to facilitate early implant fixation. Because in these prior art attempts the implant is coated during the manufacturing process, pre-application of a biologically active substance at the time of manufacture increases the cost of the surgical procedure because excessive amounts of the expensive biological factor are needed during the manufacturing process and to ensure it's long term sterility and stability. In addition, pre-applying the biological substance at the time of manufacture also does not allow a surgeon to customize the amount of a biologically active substance applied to the implant for a particular procedure.
Accordingly, there is still a need in the art for a intraopertive, user-friendly, flexible, and relatively inexpensive method to facilitate early implant fixation.